The role of the hypothalamic β-adrenergic system in controlling the LH rise in short-term castrated rats

Abstract

ABSTRACT Intraventricular infusions of adrenaline and various pharmacological agents acting on β-adrenergic receptor subtypes were carried out in rats orchidectomized 16 h previously. Infusions (10 μl) of solutions containing the drugs were administered under anaesthesia induced with alphaxalone and alphadolone. Levels of LH were measured in plasma collected immediately before and at predetermined intervals after the infusion. The acute rise in LH levels after castration was increased still further by isoprenaline (a mixed β1- and β2-agonist), fenoterol (a β2-agonist) and atenolol (a β1-antagonist). In contrast, prenalterol (a β1-agonist) and (2RS,3RS)-3-isopropylamino-1-(7-methylindan-4-yloxy)butan-2-ol (ICI 118 551) (a selective β2-antagonist) were inhibitory to LH release. Adrenaline itself, salbutamol (another selective β2-agonist), propranolol (a mixed β-antagonist) and metoprolol (a β1-antagonist) did not significantly alter plasma LH concentrations at the doses administered. The stimulatory effect of isoprenaline on LH release was partially reduced when given together with ICI 118 551, but was not affected when administered simultaneously with atenolol. The inhibitory effect of ICI 118 551 was, however, prevented by concomitant administration with fenoterol, as was that of prenalterol when infused with atenolol. The results suggest that the hypothalamic mediation of the short-term changes in LH release in response to castration is exerted, at least in part, through the activation of a β2-stimulatory component and the suppression of a β1-inhibitory component. J. Endocr. (1987) 114, 167–172